Scientists are getting close to understanding the causes of Alzheimer's disease, and how the disease can be prevented, according to a leading researcher in the field.

Researchers have identified several factors that seem to increase the likelihood of the disease, a progressive mental deterioration which affects about 10 percent of all Americans by the time they reach age 75, and 30 percent by the age of 90, explained Dr. Peter Rabins of Johns Hopkins University.

Some things which seem to decrease a person's odds of getting the disease have also been identified, said Rabins, the author of the best-selling book ''The 36-Hour Day,'' a family guide to caring for persons with Alzheimer's disease, related dementias and memory loss in later life.

Rabins was in Athens Wednesday to give the keynote speech at a statewide conference on Alzheimer's sponsored by the Athens Community Council on Aging.

People who take supplemental estrogen or anti-inflammatory painkillers like Motrin and Advil seem to be at lower risk of Alzheimer's. A recent study also indicates that vitamin E can slow down the progressive deterioration of Alzheimer's, and possibly even prevent or delay its onset, Rabin indicated.

On the other hand, people with Down syndrome will develop Alzheimer's, and people who have had head injuries -- including athletes like boxers and football players -- are more at risk.

People with a history of depression may also be more likely to develop Alzheimer's, he said.

''Alzheimer's is not one disease -- we know that now,'' he said. But at the same time, scientists are focusing in on the biochemical processes that produce the symptoms of Alzheimer's.

One of the most powerful predisposing factors seems to be a single gene which accounts for about 30 percent of all cases, according to Rabin.

People with one form of the gene actually are less likely than average to get Alzheimer's. But people with another form of the same gene are much more likely to get the disease. People with one copy of the gene have a 40 percent chance of getting Alzheimer's. People with two copies on their chromosomes, on both the mother's and the father's side, have a 90 percent chance of developing Alzheimer's in later life.

All those factors together mean scientists are getting close to understanding the roots of Alzheimer's, Rabin argued.

''That offers us a lot of hope that Alzheimer's can be prevented in our lifetime,'' he said.

A little-understood protein is at the center of the memory loss, hallucinations and other symptoms that Alzheimer's patients suffer as their disease grows progressively worse, he said.

Scientists don't know what the protein does, but they do know that it breaks down as it is processed in the brain. In most people, the waste products from the process are carried away, but people with Alzheimer's cannot rid their brains of those byproducts.

''It's a garbage disposal problem,'' he said.

A fix for that genetic problem could come very soon, he predicted.

''The chance of that happening in the next five years is very good. Every drug company in America is working on that,'' Rabin said.